See the importance of post-operative monitoring in bariatric surgery to avoid a lack of nutrients in the body
Over time, bariatric surgery has become an alternative treatment for morbid obesity. For patients who have already tried a more conservative method with diet and physical activity and still failed, this procedure is an option to consider.
However, despite its long-term benefits, it is important to be aware of the risks of post-bariatric nutritional deficiency. Because of the anatomical and physiological changes common with bariatric procedures, patients who opt for this solution are more likely to develop nutritional complications.
In this article, you’ll learn a little about the causes of these nutritional deficiencies after stomach reductionIn addition, you should know which nutrients are most affected and the importance of nutritional monitoring after surgery. To find out more, contact Dr. Carlos Obregon, gastro-surgeon at Instituto Medicina em Foco.
Malnutrition after bariatric surgery: what are the factors?
First of all, it should be pointed out that surgical techniques in the bariatric procedure are neither purely restrictive nor disabsorptive. In the past, this concept was common (the Adjustable Gastric Band – AGB – was purely restrictive while the duodenal switch and scopinaro were dysabsorptive), but today this has changed.
Currently vertical gastrectomy (gastric sleeve) removes approximately 80% of the stomach volume. This removes an area that is extremely important in modulating appetite: the gastric fundus – the region that produces the hunger hormone ghrelin. This causes the patient to have a lower appetite.
O bypass is not a dysabsorptive surgery in most patients, at least as far as macronutrients (carbohydrates, fats and proteins) are concerned. An intestinal detour does occur, but the part destined for absorption (common loop) is much larger than in disabsorptive procedures.
On the other hand bypass patients may experience micronutrient dysabsorption (minerals – such as iron, copper, zinc and vitamins – A, D, K, B complex). But the main mechanism of bypass weight loss is not dysabsorption, but hormonal stimulation. Thus, bariatric surgery can lead to the development of macro and micronutrient deficiencies after surgery as has been shown in some studies.
In addition, a factor that contributes to this malnutrition is the lack of nutritional follow-up after surgery. According to a survey published in Oxford AcademicAccording to the study, only 29.6% of bariatric patients returned for a consultation five years after surgery. Similar data was reported in another study which showed that only 80 out of 1216 patients were receiving follow-up care in the third year.
Other factors that increase the risk of vitamin deficiencies in bariatric patients
- Significant reduction in calories in the diet, even with an increase in protein consumption.
- Changes in the structure and functioning of the digestive system.
- Imbalances in the intestinal flora after surgery.
- Absence or inadequate use of essential nutritional supplements.
SIBO: a factor that can occur in some bariatric patients
Some types of bariatric surgery, such as gastric bypass, increase the risk of Small Intestine Bacterial Overgrowth (SIBO). This condition may already be present in people with obesity before the operation.
In a study of 378 patients, SIBO was identified in about 15% of subjects before surgery and increased to 40% after Bypass surgery. In addition, bacterial overgrowth compromises nutrient absorption, competing for vitamins and minerals, and its metabolites can damage the intestinal lining. This can cause deficiencies in fat-soluble vitamins (A, D and E), proteins, carbohydrates, thiamine and vitamin B12, while folate and vitamin K levels tend to rise.
If you have undergone bariatric surgery, contact MEF and make an appointment with Dr. Carlos Obregon.
Post-bariatric nutritional deficiency: what problems are possible?
Post-surgery, it is common for some bariatric patients to report some nutritional problems. Take a look at the most common ones.
Anemia
A anemia is one of the most frequent deficiencies after bariatric surgeryespecially in the first two years. According to the American Society of Hematology, between 33% and 49% of bariatric patients develop anemia during this period. It is worth remembering that up to 12% of patients already have anemia before surgerywhich reinforces the importance of carrying out preoperative screening tests.
This post-bariatric anemia is usually related to iron deficiencycaused by factors such as
- Reduced food intake.
- Intolerance to meat or dairy products.
- Decreased gastric acidity (hypochlorhydria).
- Deviation of the duodenum and proximal jejunum, fundamental regions for iron absorption.
In addition to iron vitamin B12 can also be lacking, especially after intestinal bypass surgeries, such as bypass surgery. This vitamin depends on the duodenum and the intrinsic factor to be absorbed – structures that are altered in these procedures. A oral or intramuscular B12 supplementation is indicated in many cases.
Another important cause of anemia is folic acid deficiency. It reaches from 9% to 39% of bariatric patientsalso contribute to fatigue and a drop in immunity.
Problems with bone metabolism
Bariatric surgery can have a direct impact on bone healthincreasing the risk of osteoporosis, loss of bone mass and fractures. This is because, in addition to the reduction in the mechanical load on the bones after losing weight, there is difficulty in absorbing calcium and vitamin Dessential nutrients for maintaining a strong bone structure.
The main causes of this bone fragility include:
- Detour of the duodenum and jejunumwhere calcium is absorbed.
- Reduced activation of vitamin Daggravated by fat malabsorption.
- Low dairy intakefrequent vomiting or failure to supplement.
To prevent complications, it is essential to maintain adequate levels of calcium and vitamin Dwith targeted supplementation and regular examinations to monitor bone mineral density.
Vitamin and mineral deficiencies
After bariatric surgery, it is common for the body to experience low absorption of vitamins and minerals, especially in procedures with intestinal detour. See the main deficits:
- Vitamin Acan affect up to 69% of patients after a few years. The most common symptoms are night blindness, dry eyes e hair loss.
- Vitamin Kdeficiency reported in up to 60% of cases. Normally, without visible symptomssuch as bruising or bleeding.
- Vitamin B1 (Thiamine)can affect up to 49% of patients. The lack is more noticeable in patients who have been through the jejunal bypass. It can develop into Wernicke-Korsakoff syndromewith severe neurological symptoms.
- Vitamin Cdeficiency in 10% to 50% of patients. It can cause slow healing, petechiae e bleeding gumsalthough there are not always clear signs.
In addition to vitamins, surgery can compromise the absorption of essential minerals such as zinc, magnesium, copper and selenium. These nutrients participate in various functions in the body and their lack can affect the nervous system, heart and intestines. Regular check-ups are essential to detect and correct these deficiencies.
Protein malnutrition
A protein malnutrition is one of the most serious complications after bariatric surgery, especially in procedures with malabsorption. After Biliopancreatic diversion (BPD)the incidence can reach 21% of patients. In gastric bypassthe risk increases when the Roux limb exceeds 150 cm, with records of up to 13% over two years.
Even in more restrictive surgeries, such as the gastric sleevemalnutrition can occur in patients who:
- They avoid eating protein-rich foods.
- They experience frequent post-operative vomiting.
- They develop inappropriate eating behaviors.
Protein deficiency can lead to a drop in albumin in the blood, edema, loss of strength and increased risk of hospitalization. The evaluation of lean body mass and monitoring protein levels are key to detecting the problem early and adjusting diet or supplementation.
How important is quality nutritional care in the post-operative period?
This is why specialized nutritional monitoring is essential to prevent deficiencies that can compromise the patient’s physical and emotional health. Without proper guidance, deficiencies in iron, calcium, vitamins B12, D and A are common, as well as loss of muscle mass and protein malnutrition.
A nutritionist with experience in post-bariatric surgery evaluates the evolution of the diet, adapts the diet to the needs of each phase, guides supplementation and requests tests for regular monitoring. This continuous care helps to maintain a healthy weight, prevents clinical complications and improves quality of life in the long term, promoting a safe and effective process of dietary re-education.
Why trust Instituto Medicina em Foco for post-bariatric medical care?
In Institute of Medicine in FocusThe care of bariatric patients goes beyond surgery. Here, your journey doesn’t end right after the procedure – it’s in the post-operative period that medical follow-up becomes even more important to preserve health, avoid nutritional deficiencies and ensure sustainable long-term results.
With a team of specialized nutritionists and clinicians, the Institute offers a complete care plan, focusing on preventing complications and adapting to diet.
Post-bariatric care at the Instituto Medicina em Foco offers:
- Up-to-date gastrosurgeons and experienced in cases of post-bariatric nutritional complications.
- Nutritionists specializing in bariatrics and nutritional supplementation.
- Frequent laboratory tests and bioimpedance examination.
- Prevention and correction of deficiencies in iron, calcium, vitamins B12 and D.
- Monitoring weight loss and body composition.
- Individualized and humanized care plans.
Dr. Carlos Obregon, MEF gastrosurgery specialist
Dr. Carlos Obregon was born in Minas Gerais and graduated in Medicine from the Federal University of Uberlândia (UFU). In São Paulo, he completed his medical residency in General Surgery and Digestive System Surgery at the University of São Paulo Medical School (FMUSP).
He currently works as a collaborating doctor at the Colon and Rectum Surgery Service of the Hospital das Clínicas (HCFMUSP) and as a surgical on-call doctor at the Cancer Institute of the State of São Paulo (ICESP-HCFMUSP).
Schedule your appointment at Instituto Medicina em Foco
If you need to make an appointment with a multidisciplinary team for nutritional monitoring, contact MEF and ask Dr. Carlos Obregon your questions. Don’t hesitate to get in touch.
Book your appointment here with MEF’s gastro-surgeon and multidisciplinary team in São Paulo.
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Content updated in 2025.
FAQ – Frequently asked questions about post-bariatric nutritional deficiency: learn about the risks
1. What tests are evaluated during the consultation with the gastro-surgeon in the post-bariatric period?
Laboratory tests, vitamin levels and body composition are evaluated to monitor health after bariatric surgery.
2. Is it true that bariatric surgery can cause nutritional deficiencies if not monitored?
Yes. Without follow-up, bariatric surgery can cause serious nutritional deficiencies, such as a lack of vitamins and minerals.
3. How does nutritional monitoring work after gastric sleeve?
Post-gastric-sleeve monitoring guides diet and supplementation, preventing nutritional deficiencies.
4. When should I worry about signs of post-bariatric malnutrition?
Weakness, hair loss, dizziness and loss of lean mass can indicate malnutrition after bariatric surgery.
5. Why is it important to replace vitamins such as B12 and D after bariatric surgery?
Vitamins such as B12 and D are poorly absorbed after bariatrics, so continuous replacement is essential.
6. How does consulting a nutritionist after bariatrics help with supplementation?
The nutritionist adjusts the diet and supplements according to the tests, preventing nutritional deficiencies.
7. What is the risk of iron and calcium deficiency after bariatric surgery?
After bariatrics, there may be malabsorption of iron and calcium, increasing the risk of anemia and osteoporosis.
8. How can I tell if I’m losing muscle mass after bariatrics?
Tiredness, loss of strength and bioimpedance results can indicate loss of muscle mass after bariatrics.
9. Can a lack of follow-up lead to protein malnutrition in bariatric patients?
Yes. Lack of follow-up can cause protein malnutrition, affecting immunity and recovery.
10. Do people who have been morbidly obese need to maintain long-term nutritional supplementation after surgery?
Yes. Even after losing weight, supplementation should be maintained to avoid nutritional deficiencies in the long term.
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